The magnetorheological (MAR) medical brace includes a flexible outer shell that fits around the anatomical area to be braced and a plurality of adjustable straps for securing the shell onto the anatomical area. The shell encases a MAR pack filled with magnetorheological fluid or gel. A plurality of magnets is attached to or encased in the shell to provide magnetic field acting on the MAR pack. The interaction of the magnetic field with the MAR pack adjustably increases or decreases the stiffness of the shell depending on the strength of the magnetic field. A control mechanism is provided for selective adjustment of the magnetic field and other functions.